REST API Document upload size limit (simple method)

Hi experts,

My colleagues are working on using the REST API for file uploads to OTCS, but the version in place at customer is still 16.2.11, which doesn't have the v2 large file upload option per documentation. The developers are battling to upload files larger than an couple of MB from what I've heard- do you know what the size limit is for the simple upload POST call?

[The customer as an upgrade to latest version on the agenda in next calendar year, but they need to get the integration piece proven out now]